Researchers from Siberian Federal University with participation of their colleagues from the Institute of Chemistry and Applied Chemistry (Siberian Branch, Russian Academy of Sciences) have conducted experiments on growing thick diamond films. The researchers have managed to get amorphous films with ordered orientation of diamond molecules.
The diamond is of interest to researchers as it possesses a wide range of limit properties. This is the strongest of known materials, it almost does not enlarge under heating, it is chemically inert and wearproof, it possesses low friction coefficient and high thermal conductivity, and is also optically transparent in a wide spectrum range. Continuous diamond films can be used as a chip substrate for taking heat off, as abrasives and covering for cutting tools. An extra-hard diamond film is able to protect movable parts of mechanisms from abrasion. Due to its optical properties, the diamond film can serve a protective coat for infrared optical instruments and devices under unfavorable environmental conditions.
The Siberian researchers represent any diamond crystal in the form of a combination of the Diam diamond nanocubes, each of them consisting of 104 carbon atoms. Such ideally identical cubes can easily pave any surface and both a monocrystal and a diamond film can be assembled of them.
Superdispersed diamonds are obtained via explosion of carbonic substances. To grow a thick diamond film, the researchers get a combination of diamond nanocubes with potassium hydroxide and anneal it at the 300°С. Alkali well refines diamond particles surface from admixtures. Then potassium hydroxide is washed out by distilled water, which forms as a result nanodiamond water dredge. Most of this dredge accumulates on the bottom, thus forming a phase that can be called liquid phase. Above it, there is a phase that consists of the Diam diamond molecules, freely floating in the water. This phase the experimentalists precipitated on chips of silicon crystals heated up to 300°С.
Diamond cubes suspended in the water drip on the substrate and spread upon it, forming a film. The rate of increase for such a film makes about 1 Angstroem unit per second, but at this stage of investigation, the researchers did not face the task of getting high growth films (economically profitable rate of increase for the diamond film should make several hundred microns per hour). Some film samples turned out to be rather thick – about 1,000 Angstroem units.
As preliminary investigations have proved, thermal conductivity of surface areas with the film is twice higher than that without a film. The films are resistant to acids, they do not dissolve in the hydrofluoric acid. Besides, adherence energy and film solidity are also very high: they can be hardly taken off by a metal broach file, as it glides and breaks silicon under strong pressure. All these testified to a certain extent to availability of a diamond film, possibly, even a monofilm. However, the researchers have failed so far to fully get rid of alkali. The obtained films represent amorphous compounds of alkali and Diam with ordered thickness orientation of diamond nanocubes.